1. Field of the Invention
The invention relates to a contact terminal for a circuit board in which a contact spring piece is projected to the outside of the terminal so as to make contact with a circuit board.
2. Related Art
FIGS. 7 and 8 depict a contact terminal for a circuit board which is disclosed in Unexamined Japanese utility model publication No. HEI 5-62972.
In the contact terminal 25, an opening 3 is formed in a bottom plate portion 2 so that a contact plate portion 27 of a spring piers 26, which is continuously raised from the bottom plate portion 2, is projected through the opening 3. The spring piece 26 comprises a sloped portion 10 which is raised from the bottom plate portion 2, a flat plate-shaped contact plate portion 27, which is downwardly bent from the sloped portion 10 and is positioned in a substantially horizontal manner in a free standing state, and a rear plate portion 28 which is upwardly bent from the contact plate portion 27 and has, at the tip end, a perpendicularly elongated stop plate 12.
A contact projection (indent) 29 having a substantially hemispherical shape is sweat welded onto the contact plate portion 27. As depicted in FIGS. 9 and 10, the contact projection 29 makes contact with a counter circuit board 18. Specifically, when the contact terminal 25 is inserted into a connector housing 17, as shown in FIG. 9, the sloped portion 10 of the spring piece 26 simultaneously butts against butting wall 20 inside the housing, so as to be directed downwardly, resulting in the contact plate portion 27 being projected through the opening 3. The stop plate 12 butts against the bottom plate portion 2, thereby restricting the amount of the contact plate portion 27 that is projected through the opening.
Subsequently, as shown in FIG. 10, the circuit board 18 is inserted into the connector housing 17 along the contact plate portion 27, and then slidably contacts with the contact projection 29. The contact plate portion 27 is marginally disposed upwardly by the circuit board 18 So that the stop plate 12 is disposed upwardly and loses contact with the bottom plate portion 2.
However, the above-described structure of the prior art has the following drawback. In FIG. 10, the tip end 18a of the circuit board 18 butts against the contact projection 29, thereby producing concerns that the spring piece 26 is deformed, that circuit elements on the counter circuit board 18 are shaven off, and that the contact of the insertion of the counter circuit board 18 is impaired. In the case where, as shown in FIGS. 11 and 12, the spring piece 26 is pushed in the projection direction by an operation such as the insertion of the contact terminal 25 into the connector housing 17, if the stop plate 12 is too short, there arises a concern that the spring piece 26 is deflected and deformed and the stop plate 12 easily slips off the opening edge 2a of the bottom plate portion 2.